The present disclosure relates to ink jet ink compositions and ink jet printing processes. More specifically, the present disclosure relates to ink jet compositions comprising novel anti-curl agents suitable for use in multi-color ink jet printing processes.
Ink jet printing is a non-impact printing method that produces droplets of ink that are deposited on a print substrate such as paper or transparent film in response to an electronic digital data signal. Thermal or bubble jet drop-on-demand ink jet printers have found broad applications as output for personal computers in the office and in the home.
In existing thermal ink jet printing processes, the printhead typically comprises one or more ink jet ejectors. Each ejector includes a channel communicating with an ink supply chamber, or manifold, at one end and an opening at the opposite end, referred to as a nozzle. A thermal energy generator, usually a resistor, is located in each of the channels at a predetermined distance from the nozzles. The resistors are individually addressed with a current pulse to momentarily vaporize the ink within the respective channel to form a bubble that expels an ink droplet. As the bubble grows, the ink rapidly bulges from the nozzle and is momentarily contained by the surface tension of the ink as a meniscus. This is a very temporary phenomenon, and the ink is quickly propelled toward a print substrate. As the bubble begins to collapse, the ink still in the channel between the nozzle and bubble starts to move towards the collapsing bubble, causing a volumetric contraction of the ink at the nozzle and resulting in the separation from the nozzle of the bulging ink as a droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides the momentum and velocity for propelling the droplet in a substantially straight line direction towards a print substrate, such as a piece of paper. Important properties of the ink in this context include the ink's viscosity and surface tension. Subsequently, the ink channel refills by capillary action and is ready for the next repeating thermal ink jet process. Thermal ink jet processes are well known and described in, for example, U.S. Pat. Nos. 4,251,824, 4,410,889, 4,412,224, 4,463,359, 4,532,530, 4,601,777, 5,139,574, 5,145,518, and 5,281,261, the entire disclosures of which are incorporated herein by reference. Because the droplet of ink is emitted only when the resistor is actuated, this type of thermal ink jet printing is known as “drop-on-demand” printing.
Another type of drop-on-demand ink jet printing is called piezoelectric ink jet printing. This ink jet printing system has an ink filled channel with a nozzle on one end and a regulated piezoelectric transducer near the other end to produce pressure pulses according to the digital data signal.
A third type of drop-on-demand ink jet printing is called acoustic ink jet printing which can be operated at high frequency and high resolution. The ink jet printing system utilizes a focused acoustic beam formed with a spherical lens illuminated by a plane wave of sound created by a piezoelectric transducer. The focused beam reflected from a surface exerts a pressure on the surface of the liquid ink, resulting in ejection of small droplets of ink onto an imaging substrate. Aqueous ink jet inks can be used in this printing system.
An ink jet printing method that is different from the drop-on-demand ink jet printing is called continuous ink jet printing. In this ink jet printing system, ink is emitted from a nozzle in a continuous stream under pressure. The stream is ejected out of an orifice and perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break up point, the electrically charged ink droplets are passed through an applied electrode which is controlled and switched on and off according to the digital data signals. The charged ink droplets are passed through a controllable electric field which adjusts the trajectory of each ink droplet in order to direct it to either a gutter for ink deletion and recirculation or a specific location on a print substrate to create an image. Multiple orifices or nozzles can be used to increase imaging speed and throughput.
In an ink jet printing apparatus, the printhead typically comprises a linear array of ejectors, and the printhead moves relative to the surface of the print substrate, either by moving the print substrate relative to a stationary printhead, or vice-versa, or both. In some types of apparatuses, at least a relatively small print head supplied with an ink moves across a print sheet numerous times in swaths in order to complete an image. For multicolor ink jet printing, a set of printheads and ink (e.g. cyan, magenta, yellow and black) can move across the print substrate numerous times in swathes and disperse selected inks in any desired pattern (e.g., ⅛, ¼, ½, fulltone (1/1)) according to digital signals. The speed of this type of single or multiple color ink jet printing on a substrate is determined by the moving speed of the printheads across the print substrate, ink jetting frequency (or frequency response), and the desired number of swathes needed for printing. The printing speed of this type of ink jet apparatus can be increased if two or more print heads are budded together to form a partial-width array printhead for printing each ink in a monochrome or multicolor ink jet printing system. The partial-width ink jet printhead has more ink jet nozzles per printhead, and can deliver a large number of ink droplets across the substrate in a swath in a short period of time. Monochrome or multicolor ink jet printing apparatuses using one or several partial-width printheads may have a faster printing speed than current commercial ink jet printers.
Alternatively, a printhead that consists of an array of ejectors (e.g., several butted printheads to give a full-width array printhead) and extends the full width of the print substrate may pass an ink down once onto the print substrate to give full-page images, in what is known as a “full-width array printer”. When the printhead and the print substrate are moved relative to each other, image-wise digital data is used to selectively activate the thermal energy generators in the ink jet printhead over time so that the desired image will be created on the print substrate at a fast speed. For multicolor ink jet printing, several full-width array printheads and inks (e.g., cyan, magenta, yellow, and black) can be used to deliver multiple color inks onto a print sheet. This type of multicolor ink jet printing process is capable of printing multiple color images and monochrome color images on a print substrate at a much faster speed (e.g., more than five pages of full color images per minute) than current commercial color ink jet printers.
In multicolor ink jet printing processes, several inks can be printed on a print substrate. In some instances, two different inks can be printed next to each other. Intercolor bleed can occur if the inks are not dried properly or if the printing process is too fast for the inks to set. Undesired ink mixing on a print substrate, especially on the surface of a plain paper, can cause distorted images near the border of two inks. After the inks dry, the border of the two inks can appear irregular with poor edge sharpness (or raggedness) due to the invasion of one ink into the other. Such bleed images are visibly unattractive. This phenomenon is generally called intercolor bleed (ICB). Intercolor bleed occurs particularly when a darker colored ink (such as a black ink) and a lighter colored ink (such as a yellow ink, a cyan ink, a magenta ink, or the like) are printed next to each other because of the high contrast between the two colors. Intercolor bleed can also occur when two color inks are printed next to each other (for example yellow ink next to magenta ink, yellow ink next to cyan ink, magenta ink next to cyan ink or the like). The severity of the intercolor bleed generally is affected by the ink type and composition, absorption rate of the printer substrate, printhead design, ink drop mass, ink dot size and method and speed of printing. As a result, there is a need to reduce intercolor bleed and to produce high quality multicolor ink jet images on print substrates, including plain and coated papers, transparencies, textiles and other desired substrates.
In the thermal ink jet printing water is usually a key component, which is responsible for the bubble formation and propelling the ink out of nozzles toward the imaging substrate (print sheet). The use of water in large concentrations, however, has also some disadvantages. Water has a fast evaporation rate relative to high boiling organic solvents (e.g. humectants, anti-curl agents, etc.). Ink ingredients such as water soluble or water compatible dyes, pigments, biocides, and other chemical additives may become destabilized due to the loss of water during idling time. As a result printheads may become plugged, which produce some jetting failure.
Water also interacts with paper to cause two major distortions known as paper cockle and paper curl. Paper cockle is a distortion in which bumps, indentations and other irregularities are randomly produced on the printed paper, giving the paper a “wrinkled” appearance.
Curl is a phenomena in which the edges or corners of the paper migrate towards (toward imaging side) or away from (away from the imaging side) the center of the paper. Generally, the term “curl” refers to the distance between the base line of the arc formed by a recording sheet when viewed in cross-section across its width (or shorter dimension—for example, 8.5 inches in an 8.5×11 inch sheet, as opposed to length, or longer dimension—for example, 11 inches in an 8.5×11 inch sheet) and the midpoint of the arc. This type of curl applies to long grain cut paper, since curl is typically perpendicular to the process direction of a paper making machine. To measure curl, a sheet can be held with the thumb and forefinger in the middle of one of the short edges of the sheet (for example, in the middle of one of the 8.5 inch edges in an 8.5×11 inch sheet) and the arc formed by the sheet can be matched against a pre-drawn standard template curve. Such curl measurement is referred to as “hanging radius curl.”
Curl is possibly caused by the printed aqueous ink on one side of the paper releasing stress on the surface of the paper which induces a differential paper stress or uneven stress between top and bottom surfaces for the paper after drying and aging. The direction of curl may be toward the printed (imaged) side of the paper, or it may be toward the non-printed (non-imaged) side. Application of liquid inks that contain water to paper causes an initial hydroexpansion of the fibers of the paper. This initial hydroexpansion causes an expansion curl away from the image which occurs typically right after printing. Steady state curl, also known as cool curl, is toward the image, and typically occurs over a period of time when the sheet tries to achieve a state of final stress release after being dried. Active drying accelerates the effect of towards the image curl or steady state curl. For the purpose of this disclosure, paper “curl” is defined as including both curling and cockling of the paper substrate.
Curl may appear immediately after printing or may take a day or two to manifest. In its final state, the paper sheet in a severe case may take the form of a tube, a roll, or a scroll. Curled paper cannot be stacked sheet upon sheet, thereby causing much inconvenience to the user. Curled sheets are difficult to display or store and cannot be used in processes requiring near planarity, such as media feeding, tracking, and print alignment. Curl is most prevalent in solid area printing and is therefore a more acute problem in graphics than in text printing. For the same reason, it is also a concern in four color printing especially when it involves printing composite colors or where graphics are prominent. Curl is also a problem when a large quantity of ink is needed to achieve high optical density images.
The severity of the paper curl may be affected by the property of the plain and coated paper substrates, the type of aqueous ink used in the printing, temperature of the substrate during printing, and the ink jet printing process. Papers that have a small built-in differential stress between the top and bottom surfaces in the paper manufacturing process may provide little curl after ink jet printing. On the other hand papers with a large built-in differential stress between the top and bottom surface will tend to exhibit significant paper curl after ink jet printing. The degree of differential stress that is built into the papers depends on the conditions of the paper manufacturing process. Papers that are thicker or heavier and have a stronger mechanical strength tend to give lower degree of paper curl as compared to those thinner papers with weaker mechanical strength. Once a paper used in the ink jet printing is selected then the fate of curl formation is somewhat fixed. Some papers will develop curl much easier than others. In an ordinary office environment, plain and coated papers are used in the ink jet printing. Depending on the paper supply situation in the office, a customer may not have a chance to select a proper paper with a smaller curl property for the ink jet printing. Thus, there is a need to have a process that reduces paper curl with minimum impact from the paper.
Inks having a large amount of anti-curl agent may reduce the curl. However, the use of the required amount of the anti-curl agents in the inks, which is generally in excess of 10% by weight of the ink composition, may increase the viscosity of the ink and cause great difficulty in jetting the inks, especially after some idling in a printhead. This is especially true when water evaporates near the nozzles during idling time, resulting in a dramatic increase in ink viscosity and possible jetting failure. Water evaporation during idling time can also cause crystallization and precipitation of dyes or agglomeration of pigments. Most of the anti-curl agents have high boiling point and high viscosity. Thus, the use of high viscosity anti-curl agents in required large quantities may cause short ink latency and increase jetting difficulty. This is especially true when a high resolution ink jet printhead is used, which has a narrow nozzle opening (about 10 to 49 microns for a 400 and 600 spots per inch resolution printhead as compared to greater than 49 microns in a 300 spots per inch resolution printhead). Due to these aforementioned limitations there is a need to develop a process for the ink jet printing whereby ink jet printing of solid area images for graphic applications can be easily carried out to give reduced paper curl.
In ink jet printing, it is desirable to reduce the consumption of paper for economic and environmental reasons. Duplex printing sometimes may be desired. However, if a paper has been printed with aqueous ink jet images having solid areas the paper may form curl or cockle, which prohibits smooth paper feeding in subsequent ink jet printing. Thus, printing duplex (on two sides of a paper) can be difficult if the imaged paper is not treated quickly after printing. Paper curl progressively becomes worse upon aging after printing. There is a need to provide a means for both single sided ink jet printing and two sided (duplex) ink jet printing to provide images on papers with reduced curl.
Ink jet printing (checkboarding or single pass) may also affect paper curl in multiple color printing especially printing that involves a solid area image. There is also a need to provide a decurling process to reduce paper curl.
Depending on the type of color images printed, paper curl caused by aqueous ink jet inks may vary. For example, printing blue, green and red images on a paper requires the use of several inks (e.g., 200% of normal ink coverage) which is significantly more than when printing single color cyan, magenta and yellow images (e.g. 100% of normal ink coverage). As a consequence, the printing of solid area images of blue, green and red (composite colors) create a greater paper curl problem than those of single color images (e.g., cyan, magenta and yellow). Increased curling also can be found when solid areas of images are printed in a single pass mode rather than multiple passes (e.g., checkerboarding) mode.
The permanence issue in thermal ink jet prints is usually related to the waterfastness, lightfastness and to a lesser extent the cool curl of plain papers which shortfall relative to traditional Xerography. Direct marking in thermal ink jet printing, however, does not benefit from fusing temperatures that essentially “iron out” curl issues in Xerography and must provide curl control through ink formulation. Cool curl control on plain papers remains a high priority for the Aruba and Caribbean refresh products and is an issue for Martinique products. Currently, cool curl is essentially not controlled, but merely delayed in formulations that contain up to 10% acetyl ethanolaine (AEA) or trimethylolpropane (TMP). This problem is readily observed in large solid areas of printed colors and causes plain papers to undergo dramatic scrolling.
In an effort to reduce cockle and curl in ink jet printers, efforts have been made to provide anti-curl and anti-cockling agents to reduce this problem. For example, U.S. Pat. No. 5,356,464 to Hickman et al. describes anti-curl agents at a desired amount that may be utilized in ink jet inks. However, such anti-curl agents negatively affect the stability of inks by increasing the viscosity. Such inks decrease latency and increase clogging of ink jet printhead nozzles.
U.S. Pat. No. 5,207,824 to Moffatt et al. describes an ink jet ink comprising an anti-cockling agent for thermal ink jet printers. In some cases, the use of a required amount of anticockling agents in the inks to reduce curl tends to aggravate the nozzle pluggage and jetting failure. This is possibly due to their contribution of the viscosity increase of inks and incompatibility of ink ingredients with some dyes or pigments. The effective use of anticockling agents in ink sometimes may be limited.
Dendrimers, which have highly branched architectures, have been used as low viscosity additives to improve binding and smear resistance in ink jet inks. The use of dendrimers in ink compositions is disclosed in, for example, U.S. Pat. Nos. 5,120,361 and 5,266,106, the entire disclosures of which are incorporated herein by reference. DSM has developed a poly(propylene imine) dendrimer, currently available under the name ASTRAMOL™. However, dendrimers are typically prepared in low volumes by the stepwise, controlled synthesis of very regular structures. The stepwise synthesis of dendrimers generally involves protect-deprotect strategies and purification procedures at the conclusion of each step. Consequently, synthesizing dendrimers can be a tedious, difficult and expensive process.
There is thus a need in the art for new methods of reducing curl in printed paper for ink jet printers. There is also a need for ink jet printers that utilize aqueous inks and clear aqueous liquids that can reduce paper curl.
A need also exists in the art for a printing process that allows printing in full page graphics/text without producing paper curl with inks having high pigment concentrations. There is a further need for a process, an apparatus and ink jet inks that provide enhanced print quality in high resolution printers without causing undesired curl of the printed materials.